The present invention relates to a vacuum pump and in particular to a device that is capable of creating a source of vacuum from a source of compressed air.
Frequently the situation arises where there exists an abundant supply of compressed air but a shortage of vacuum pressure. This situation typically occurs in trucks, and especially those which are diesel powered. Since many of the accessory devices installed on trucks are vacuum actuated, the need for an adequate supply of vacuum pressure can be readily appreciated. The present invention is particularly suited for such applications, because of its ability to generate as much vacuum pressure as is required to actuate a particular vacuum load. In addition, the construction of the vacuum pump according to the present invention is designed to be relatively inexpensive, so as not to add significantly to the cost of the vehicle.
Generally speaking, the vacuum pump comprises a single acting piston that is adapted to draw air from a vacuum load into a vacuum reservoir under the power of a power return spring that is cocked by the piston during its compressed-air-actuated power stroke. The pump is adapted to cycle as often as is necessary to satisfy the demand of the vacuum load. Stalling in very slow movement modes of operation is prevented by a unique dumping valve arrangement that is adapted to cause a sudden increase in the pressure differential across the piston at the end of the piston's return stroke. A valve train assembly comprising an inlet valve and an exhaust valve is provided which is actuated at the termination of the piston stroke in each direction. The valve train assembly controls the input and exhaust of the compressed air which powers the piston on its power stroke.
Additional objects and advantages of the present invention will become apparent from the following detailed description of the preferred embodiment which makes reference to the following drawings.